This invention relates to brake control systems for governing field pressure control of friction brakes of a vehicle, and while the invention is subject to a wide range of applications, a preferred embodiment of the invention will be particularly described as applied to a fluid brake control system having an improved electro-pneumatic pilot valve device.
It is general practice in controlling brakes of electrically propelled rapid transit cars, light rail vehicles, and the like, to govern braking on each car in accordance with an analog signal indicative of total braking requirements. This can be a variable fluid pressure signal or a variable electrical signal in accordance with the type of braking system employed. Such an analog signal may be indicative of total braking requirements to be provided for the vehicle, in part by dynamic braking, and in part by fluid actuated friction brakes. An electro-pneumatic pilot valve device is used to generate a pilot signal indicative of the extent of friction braking that is required to supplement the dynamic braking. This pilot signal is generally used to govern the friction brakes through a suitable relay valve device. Electropneumatic pilot valve devices for performing this function are disclosed in the prior Engle U.S. Pat. Nos. 3,536,360, 3,536,361 and 3,924,902, and in the Bohusch U.S. Pat. No. 4,021,079, all of which are assigned to the assignee of this application. These patents are incorporated herein by reference to an extent necessary to disclose prior art details that may be considered essential for an understanding of the present invention.
The systems according to the above patents, when used for blending purposes, require an electrical torque motor, a pneumatic torque motor, a comparator shaft for comparing outputs of both torque motors, a pilot valve assembly driven by rotation of the comparator shaft, and a main valve assembly governed by the pilot valve assembly. These patents teach that different types of electro-pneumatic pilot valve devices must be used in accordance with whether the analog brake control signal input to the device is a variable fluid pressure signal or a variable electrical signal.
An object of the present invention is to provide a brake control system which substantially obviates one or more of the limitations and disadvantages of the described prior systems.
Another object of the present invention is to provide in improved electro-pneumatic pilot valve device that is universal in its application in that it can be used without modification in response to either an analog fluid braking signal input or an analog electrical signal input, either signal being indicative of total braking requirements.
Another object of the present invention is to provide an improved, simplified and less expensive electro-pneumatic pilot valve device.
Other objects, purposes and characteristic features of the present invention will be in part obvious from the accompanying drawing and in part pointed out as the description of the invention progresses.